British scientist Robert Hooke built an early microscope and was the first scientist to observe cells and give them their name. Anton van Leeuwenhoek created the best microscopes of his time and used them to study living organisms. Matthias Schleiden, Theodor Schwann, and Rudolf Virchow created Cell Theory, which says that all living things are made of cells; cells are the smallest part of a living thing; and all cells come from other cells.